This invention is directed to robots for use with molding machines, and more particularly, to a side entry robot having a take-out plate with molded article engagement means mounted on a trolley which is movable in its entirety by guides into position between mold halves of an injection molding machine and into position outside of the mold halves of the injection molding machine.
In the plastic injection molding industry, there are several types of take-out robots which are used for a broad range of applications. Depending on the application, the robot may be universal or may require a very particular design. In general, these robots may be classified based on the way they enter the molding area, i.e., through a simple translation movement such as top entry, side entry and bottom entry. Another type of take-out robot which is sometimes used consists of those which use rotation to handle and take-out a molded part. These types of robots include a swing type, pivoting type or turret type robot. In the automotive industry, legged walking robots are sometimes used for various tasks, such as that disclosed in U.S. Pat. No. 5,459,659.
The prior art includes numerous side entry robots. For application to the handling requirements of many molding procedures, these side entry robots require conceptual design modifications in order to meet such handling requirements due to over-sized and over-weight molded articles. This is particularly true in the automotive industry or when it is desired to achieve a smaller footprint on the manufacturing floor. That is, in most cases, side entry robots have been designed and used for handling a plurality of small and light molded parts.
For example, U.S. Pat. No. 4,204,824 to Paradis discloses a side entry mechanical robot which is driven in and out by the racks and gears operated during the clamp motion of the mold with which it is used. A slippable clutch is used between the racks to control the precise positions of the robot. The tooling head makes one 90.degree. flip in the out position which is achieved by a cam. Adjustable spring loaded bumpers are shown to control the end stops of the motions.
U.S. Pat. No. 33,237 to Delfer teaches a side entry, multiposition air robot which is adapted to be stopped mechanically in different "in" and "out" locations by an adjustable hydraulically controlled cylinder. The robot carries a cooled series of preform tubes to hold more than one cycle's productions of preforms. The advantage of this robot is to replace a cooling conveyor with an improved cooled robot storage plate for handling up to three cycles at a time.
U.S. Pat. No. 5,354,194 to Kresak discloses a servo driven side entry robot with a single, composite, piece-part trolley straddling a guiding/support boom. This design is especially suitable for high speed robots that could handle very light, small, single or multiple molded parts, as will be discussed below.
The patents to Paradis, Delfer and Kresak disclose very similar mechanical designs of the support means and moving means of each of the robot's take-out plate. These designs cannot be advantageously and effectively used for handling and moving large parts, such as certain molded parts in the automotive industry. For example, the robot of Kresak discloses boom means that are attached to a machine platen in a cantilever position that is prone to bending and vibrations. As shown in FIG. 1 thereof, boom means 22 is entirely positioned outside the molding area formed by mold halves 13 and 14 in a cantilevered support mode. A trolley means 23 which is displaced along boom means 22 does not enter the molding area and does not pass the lateral tiebars. In order to remove very light molded articles from the molding area, robot take-out plate 27 has been designed as a very long arm that is remotely secured in a cantilevered mode to trolley means 23. The lateral shift of the take-out plate with respect to the trolley means through the arm allows the robot take-out plate to freely reach the molding area while keeping trolley means 23 outside and very close to the lateral tiebars. This is a common and major drawback of the cantilevered type side entry robots for their application to handling large and heavy molded articles.
Referring now to FIG. 1 of the present application, a typical prior art side entry trolley robot with cantilevered connection means, similar to those discussed above, is shown. In this prior art robot, trolley means 1 is guided and travels over a distance L along boom means 2 and boom means 2 is placed outside both the molding area 3 and lateral tiebars 4. Boom means 2 is also attached to machine platen 5 in a cantilevered mode through connecting means 6 of boom means 2. Trolley means 1 do not pass by the tiebars and thus does not reach the molding area. Only the end portion 7 of take-out plate 8 comprising gripping means array 9 is moved in-between mold halves 10 to remove the molded articles. As shown in FIG. 1, a constant momentum arm M1 and a variable momentum arm M2 are generated by using this type of cantilevered take-out plate 8 and respectively cantilevered boom means 2. Constant momentum arm M1 extends between axis A--A, which passes through the center of the end portion of take-out plate 8 and up to axis B--B, that passes through the centers of trolley means 1 and connecting means 6 of the take-out plate. Variable momentum arm M2 extends between connecting means 6 and connecting means 13 of the take-out plate. Momentum reaches it maximum value when trolley means 1 reaches it outermost lateral position. Accordingly, there is a constant torque that is applied to the connecting means 6 and to connecting means 13. There is also a variable torque that is applied to connecting means 6 of boom means 2. When handling over-sized molded articles having significant weight, torque becomes a significant problem since is causes vibration and bending of the robot take-out plate and of the boom means.
U.S. Pat. No. 4,571,230 to Walker discloses a side entry robot using suction cups that enters a vertical press mold to both load and unload a vertical press with sheet molded parts, in a two-step process. For large and heavy parts, the design of the Walker robot is not advantageously applicable. That is, unacceptable torque and vibration will be generated upon arm 12 during high speed handling of molded articles, particularly heavy ones, since the mechanical design of the robot lacks stiffness.
With particular reference to the automotive industry, robots therein are intensely used to deal with tasks involving small and medium articles such as for inserting cylinder liners into cylinder blocks, as disclosed in European Patent Application 646,440; attaching a sub-assembly such as strut to the vehicle body frame, as shown in EPA 117,976; and painting and welding body parts, as shown in U.S. Pat. No. 5,412,759. As each of these robots disclose, they are designated for use with small parts or for performing tasks which do not require the lifting of large parts. The use of any of these devices applied to the molding of large parts would be unsuccessful.
The new trend in the automobile industry towards an increased use of larger and larger plastic body panels requires that the robots capable of handling these over sized parts have to be more carefully designed to meet stringent injection molding cycle times. If additional operations have to be carried out within the molding area, the final configuration of the robots need to address other handling sequences and molding scenarios as well. In this regard, reference is made to U.S. Pat. No. 5,514,427 to Ellison, that teaches a method of decorating large body panels during the molding process of the "virgin" plastic part. As shown in FIG. 1, a plastic sheet film comprising a decoration is brought from the top of the movable platen to in between the mold halves in order to inject a body part that will comprise a decorated side. As it clearly appears from FIG. 1, a top entry robot may not be capable of handling this type of large body since the decorating film is continuously supplied from a roll placed on top of the movable platen.
Another example of a molding system requiring a robot design in accordance with the present invention, is in conjunction with an injection molding machine having several mold stations placed side by side, wherein one large plastic panel has to be rapidly and very accurately transferred from one mold station to another. This system is used for sequential injection of different materials using at least two molds and here again, the robot has to be stiff, fast, and torque and vibration free.
There exists a need, therefore, for an improved side entry robot, by which vibrations and bending are substantially reduced and stiffness and reliability are increased, providing a robot capable of handling large parts.